The present invention relates to a controllable electro-optical patternable mask for controlling electromagnetic energy, particularly an electro-optical mask which utilizes electrochromic or substrate-dispersed liquid crystal cells for transmission control, and a system which involves the use of the controllable mask for use in, for example, an opthalmic surgical system such as an excimer laser system using ultraviolet electromagnetic energy for contouring the cornea through controlled ablation of the cornea, a photoresist system, a microelectronics system, or a photolithography system, as well as other types of ablation systems.
Prior art electrochromic devices are known that include a layer of an electrochromic material, such as MoO3, sandwiched between two transparent electroconductive electrode layers, for example, of indium-tin oxide(ITO). A layer of an Hxc2x1 or Lxc2x1 ion-conducting material is present between an electrode and the electrochromic material. Electrochromic devices also include devices having an ion-storage layer for storing ions. The application of an electric potential of a few volts across the electrodes causes the color of the layer stack to change. The color change is reversible.
Electro-optical devices containing an electrochromic material layer have been used in conjunction with an anti-dazzling mirror, a light control window and various kinds of display devices as described in U.S. Pat. No. 4,617,619 to Kamimari et al. Electro-optic devices utilizing the electrochromic action (i.e., induced color changes in material such as, e.g., WO3, MoO3 and V2O5) have also been studied with regard to communication systems using visible or near visible electromagnetic radiation as a message carrier. An example can be seen in U.S. Pat. No. 4,245,883. Reference is also made to U.S. Pat. No. 5,970,187 describing an electrochromic optical switching device and referring to use of the switching devices in rear view mirrors, sun roofs, architectural glass, vision control glass, displays and display screen with variable transmission. These patents are incorporated herein by reference.
U.S. Pat. No. 5,742,362 discloses a process for forming photosensitive material for the manufacture of wiring board which features an exposure apparatus comprising a liquid crystal display for displaying a mask pattern and memory means storing a transmissivity pattern with the transmissivity of each cell of the liquid crystal display element being adjusted in accordance with the transmissivily pattern. Reference is also made to U.S. Pat. No. 5,105,215 entitled xe2x80x9cLiquid Crystal Programmable Photoresist Exposure System.xe2x80x9d These two patents are incorporated by reference.
Electrochromic displays are also known and feature devices that employ a reversible electrochemical reaction to cause a change in color of segments patterned to form alphanumeric characters. Electrochromic displays are passive devices that only modulate ambient light, in contrast to an active liquid crystals that twist ambient polarized light or active light-emitting diode displays that do not modulate light but instead produce light. Hence, the electrochromic displays operate at low voltages, and have a low enough energy requirement that a watch-size display can be operated for about 1 year from a small commercial battery. In the off state, the segments are typically colorless; in the on state, they are brightly colored, for example, blue or purple.
The structure of an electrochromic display package typically consists of two substrate glass pieces, two transparent voltage electrodes, two electrochromic electrodes and one hydrophobic Li electrolyte . All pieces are held together with a solder-glass, or epoxy, seal. To operate the device, a dc potential of 1-1.5 V is applied to the voltage electrodes to activate, the electrochemical electrodes for the electrochromic oxidation and reduction process (redox reaction).
Electrochromic displays can be categorized in two types, bistable, which means that once the color has been switched, the state of the device remains, even in the absence of applied voltage. Limitations of these types of systems includes the slowness of the color change, due to the low migration ratio and the difficulties to obtain strong color changes. In the second type, two complementary electrochromic molecules are dissolved in a solvent. One becomes colored by oxidation and the other by reduction. Thus, this type of system is relatively simple to build, reacts very fast and produces dark colors.
Single layer electro-optical polymer dispersed cells have recently gained attention in the display field and work on the principle of very fine microbubbles trapped into a substrate. When no voltage is applied, the bubbles will take on a random polar orientation. Thus, if a voltage is applied to the cell the bubbles will orientate and align with the electric field, if the substrate carefully matches the index and the director for polarized light of the bubbles, the light will propagate all the way through the material without being reflected at the bubbles and without the need for polarizers.
In the field of laser surgery efforts have been made to ablate an exposed cornea in an effort to achieve a pre-determined volumetric ablation pattern to the exposed cornea. In this regard, various surgical techniques for reprofiling of the corneal surface have been proposed as described in, for example, L""Esperance, U.S. Pat. No. 4,732,14; J. T. Lin, U.S. Pat. No. 5,520,679; David F Muller, U.S. Pat. No. 4,856,513; Kristian Hohla, U.S. Pat. No. 5,520,679, these patents are also incorporated by reference herein.
In practice there are two basic techniques to ablate and remove a set volume of tissue in the cornea and they are:
1) a scanning technique that uses a small flying laser spot between 1-2 mm in diameter and requires thousands of pulses to do the surgery; and
2) a large spot beam technique wherein a laser beam of around 8 mm in cross-section is used in conjunction with an erodible mask or a moving, blocking mask to ablate and which generally requires, on average, a few hundred pulses to achieve the desired ablation.
The main advantage of a flying laser spot technique is the ability to readily execute irregular patterns. However, the flying laser spot technique suffers from the drawback of generally requiring longer surgical times to execute the desired ablation pattern both from the standpoint of the number of pulses required and the overlapping requirement to ensure coverage of the ablated area. Any increase in the length of time required to carry out the laser ablation process can lead to longer corneal exposure time and corresponding medical concerns such as cornea dehydration which can lead to poorer healing, poorer visual acuity and, in general, longer post operative recovery times. A longer time period in which a laser is operated per patient also leads to a decrease in the useful life of the laser and an increase in service requirements. Flying laser spot techniques place greater stress on the laser cavity and the optical train components due to high repetition and rate requirements.
A flying laser spot technique also leaves ridges and valleys as a result from overlapping and the resultant ablated surface will not be a highly smooth and polished ablation.
A large beam spot system does allow for more rapid application of the desired energy (including the avoidance of the degree of overlapping involved in a randomly or non-randomly applied, partially overlapping flying spot system) and typically places less strain on the laser equipment, but does not have the irregular pattern versatility provided with a flying spot system. Also, if mechanically moving components are relied upon as the means for blocking or allowing through the laser beam (e.g., an iris or rotating or sliding aperture plate, then the problems of mechanical wear, potential jamming or breakdown arise).
Attempts have been made to provide masks that operate with a large beam application including EP 0 417 952 to Rose et al. which uses a stacked set of binarily weighted masks (A to H) on a cornea intended for sculpturing. A proposed system such as this one suffers from a variety of drawbacks such as the time consumption involved in stacking and developing the mask sets and the increased potential for error brought about by a system using so many different stacked mask components.
Another example of the use of large beam application is found in U.S. Pat. No. 4,994,058 which describes a supported or contact type mask presenting a predetermined resistance to the beam such as through use of a different height erodible mask or by varying the composition of the plastic material making up the mask. A mask arrangement such as this avoids the complications of a scanning laser, but is very limited from the standpoint of having to prepare a new mask for each patient and, with respect to an erodible mask, not having the benefit of being able to test the pattern on a test strip or the like without destroying the mask. In use of an erodible mask there is also heavy reliance on chosen material consistency.
The present invention is directed at providing a controllable, patternable electro-optical mask which preferably utilizes electrochromic or substrate-dispersed liquid crystal pixel cells for transmission control of ultraviolet electromagnetic energy applied thereto. The mask of the present application has utility in a variety of fields such as use in photo refractive surgery, photoresist systems, microelectronics systems or photolithography systems. The mask is particularly well suited for use with ultraviolet electromagnetic energy utilized in an ophthamological surgical procedure such as a photo refractive keratectomy (PRK); a photo therapeutic karatectomy (PTC); or a laser in-site keratomileusis (LASIK) surgical procedure for resculpturing the exposed cornea of an eye.
Under an ophthamological application, the mask features a controllable electro-optical patternable mask system, an opthalmic laser surgery system with said controllable mask system, and a method of using the same. The apparatus and method of the present invention is particularly well suited for ablating a corneal surface using a laser in the ultraviolet spectrum and achieves extremely smooth and precise ablation surfaces with a mask system that can be repeatedly used for different patient ablation requirements. The mask is used with a large beam spot (e.g., 6-8 mm) which covers the entire projected surface on a cornea and thus avoids the time delays associated with a flying spot beam as well as ridge and valley formation. In addition to multi-patient use, the present invention avoids the delays associated with the prior art with respect to forming or assembling the mask.
Moreover, the present invention provides a system which can achieve repeated high precision or registration between the planned or predetermined ablation volume to be removed and the actual ablation volume removed so as to enable a surgeon to achieve desired levels of eyesight corrections. Also, the volumetric ablation patterns to be removed can involve highly irregular or regular configurations as an object of the present invention is to provide a system which facilitates the execution of a surgical procedure on highly irregular individual customized patterns on a patient""s cornea in addition to more regular volumetric patterns. Furthermore, the electro-optical system of the present invention can be free from the requirement of polarizing. Thus, helping to avoid the drastic 50% power loss of energy when using polarized light, and providing greater flexibility as to the power levels of the ultraviolet electromagnetic source relied upon as there is avoided the power loss which a polarizer can invoke.
The arrangement of the present invention provides a system that can achieve a customized volumetric ablation pattern based on, for example, a stored, ophthamological patient data set (e.g., a volumetric ablation data set as described in U.S. patent application Ser. No. 09/267,926 filed Mar. 10, 1999 by Dr. Luis Ruiz which application is incorporated herein) which data set is developed by a measuring instrument such as a topographer and/or aberrometer. Under the present invention, the volumetric ablation data set is provided to a processor for input to the mask system via a digital interface, for example. The matrix mask system of the present invention includes a mask which receives expanded laser energy and, based on the processed patient data, controls the energy pattern that exits in the mask for sculpturing the desired ablation pattern on the cornea or other substrate being subjected to the ultraviolet electromagnetic energy. In one embodiment of the invention, the mask of the present invention features an electro-optical component having electro-optical material which, in conjunction with other components of the mask, such as electric field generating means, is controllable to produce a pixel pattern to the applied energy so as to control the transmission of energy therethrough, and hence the ablation pattern produced on the projected surface such as the cornea of an eye.
In an alternate embodiment of the invention, the mask comprises a substrate-dispersed liquid crystal material component (e.g., encapsulated liquid-crystal micro-bubbles, within a substrate) which in conjunction with other components of the mask system such as electric field generating means, is controllable to produce a pixel pattern to the applied energy so as to control the transmission of energy therethrough and hence the ablation pattern produced on the projected surface such as the cornea of and eye. Preferably a layered sequence of first electrode layer/first substrate dispersed liquid crystal layer/second electrode layer/second substrate-dispersed liquid crystal layer/third electrode layer/third substrate dispersed liquid crystal layer/and fourth electrode layer (preferably also with outer support substrates) is provided with the orientation of the intermediate substrate-dispersed liquid crystal layer being maintained with an electric field across while the outer (first and third) electrode layers are switched between field off (full blocking mode) and field on (full transmission mode).
The multi sequence substrate-dispersed liquid crystal arrangement described above can be utilized in a variety of other devices in addition to the transmission pixel cell mask described above with a variety of electromagnetic energy spectrum levels including the visible (e.g., as a projector, anti-dazzle, rear view mirror, display device, etc.) in its ability to block and allow through the desired electromagnetic energy by, for example, manipulation of electric field generating means which preferably provides a continuous field across an intermediate substrate-dispersed liquid crystal layer while the outer substrate layers are switched between field xe2x80x9coffxe2x80x9d and field xe2x80x9conxe2x80x9d settings to achieve the desired blocking/non-blocking state.
When ablation is desired with a transmission mask under the present invention, the ablation pattern data set produced is processed by a processor such as the main computer which communicates with the mask via an interface or the like to provide corresponding commands to activate the electro-optical matrix mask. For example, in one embodiment of the invention, the transmission pixel pattern of the mask is individually controlled by the computer and is synchronized with the pulse rate of a main excimer laser. In this way, any regular or irregular ablation volume can be removed by ablating with each pulse of the large beam a set depth (based to the laser characteristics such as laser energy and density) corresponding with the matrix pattern set for that pulse. By changing the matrix pixel pattern with each large beam pulse a different ablation configuration (or the same) can be removed to achieve the desired total pattern, volume and depth.
With an excimer laser working in the ultraviolet energy spectrum, the components of the optical train are subjected to relatively high energy flux levels. In a preferred embodiment of the present invention, a large beam is expanded with a beam expander or the like positioned upstream from the active electro-optical matrix mask to lower the energy density per area received by the pixels of the mask. This avoids premature destruction of the mask. The non-blocked, transmitted portions of the large beam containing the latent image determined by the active mask are then preferably compressed with a focusing lens or the like to achieve the desired ablation profile on the projected surface being ablated.
Thus, the present invention preferably features a controlled ablation of the cornea, using ultraviolet laser radiation to achieve a sculpturing action derived from a computer driving a programmable (preferably digital based) distribution of excimer flux density across an ultraviolet computer controllable electro-optical mask as to achieve a desired volume and shape of ablation for the correction of the curvature of the cornea or for some other application as in the noted photoresist, microelectronics or photolithography fields.
The computer controllable electro-optical mask is based on a matrix array (matrix is used in a broad sense to involve any pattern suited for forming a desired ablation pattern on the ablation plane or surface) of individual electro-optical pixels with optical states between fully transparent to filly opaque or mirror like to the UV light. As noted, the ultraviolet computer controllable electro-optical matrix mask is based on transmission of electromagnetic energy passed through the mask device, with the transmission or non-transmission of light through each individual pixel being preferably controlled by an electrical voltage and a time duty cycle. In one embodiment of the invention the voltage is switched or adjusted to have the pixels either in a fully transparent or fully blocking mode with the pixel switching timing being synchronized with the laser pulse rate. In addition thereto, the frequency duty cycle per pixel can be adjusted or varied with relation to the laser pulse cycle (or with respect to the applied energy in a non-pulse situation) of the main energy source to achieve multiple on and off states of transmission during the main laser pulse cycle (or a set period of applied energy) so as to control the maximum state of ablation during that main pulse (or energy application) cycle from pixel to pixel in the mask.
In one embodiment of the invention, the electro-optical mask is an electrochromic electro-optical mask which features a plurality of controllable electrochromic cells that provide for a patternable mask system for controlling the transmission of electromagnetic radiation therethrough, The plurality of individual pixel cells are individually adjustable to different states of transmission with respect to electromagnetic radiation, and with the pixel cells including electrochromic material. The cells"" color states are determined by determining means such as a processor interfaced with said patternable mask for controlling relative transmission states between the individual electrochromic material pixel cells. In one embodiment, the electrochromic material is supported by opposite cell side UV grade support substrates for the passage of UV electromagnetic radiation to the electrochromic material of the pixel cells of said mask The pixel cells are also preferably formed from the outer pair of UV grade substrates, a pair of electrode layers and a solid layer of electrochromic material sandwiched between the electrode layers with the UV grade substrates preferably being a material selected from a group consisting of UV grade synthetic fused silica, sapphire or quartz.
In an alternate embodiment of the invention, a patternable mask system is provided for controlling the transmission of electromagnetic radiation which features a patternable electro-optical mask having a plurality of individual pixel cells with individually adjustable states of transmission with respect to electromagnetic radiation, and said pixel cells including substrate-dispersed liquid crystal material having a substrate material encapsulating dispersed liquid crystal bubbles or droplets. The mask system preferably further comprising a processor interfaced with said patternable mask for controlling relative transmission states between the individual substrate-dispersed liquid crystal material pixel cells.
The substrate dispersed liquid crystal material includes solid encapsulating substrate material (e.g., a polymer) supporting thousands of dispersed liquid-crystal droplets. The mask is also preferably comprised of an outer pair of UV grade support substrates, a pair of electrode layers and an intermediate solid layer of substrate-dispersed liquid crystal material (with the bubbles preferably being less than 5xcexc in maximum width) with one of the electrodes formed in a pixel array.
In this embodiment, as in the above noted electrochromic embodiment, the UV grade support substrate is preferably a material selected from a group consisting of UV grade synthetic fused silica, quartz and sapphire. The mask system of the present invention preferably further comprises a processor interfaced with said mask for controlling relative transmission states between said individual pixel cells and said processor which comprises means for shifting a pattern formed in said mask in conjunction with a monitored shift in a substrate to receive electromagnetic energy transmitted through said mask.
The present invention also features a mask that comprises pixel cells each with multiple substrate-dispersed liquid crystal material members (preferably solid state layers) with an electrode layer dispersed between said members and to opposite, free sides of the preferably stacked substrate-dispersed liquid crystal material members. In one embodiment, the mask system includes pixel cells having, in series, a first outer support substrate, a first electrode, a first substrate dispersed liquid crystal member, a second electrode, a second substrate-dispersed liquid crystal member, a third electrode, a third substrate-dispersed liquid crystal layer, a fourth electrode, and a second outer support substrate all of which are transparent and assembled as a monolithic unit. This embodiment also preferably includes electric field generating means for maintaining an electric field across said second, intermediate substrate dispersed layer and for switching between an off electric field state for said first and third substrate-dispersed layers and an on electric field state for said first and third substrate-dispersed layers so as to place, in the latter mode state, said first, second and third substrate-disperse layers in a transmission state.
The present invention also features a laser system for ophthamological surgery, comprising a laser and an electro-optical mask having a plurality of individual pixel cells positioned for receiving a laser beam output by said laser with said individual pixel cells having adjustable transmission states for forming a refreshable transmission pattern with respect to the laser beam received from said laser. In one embodiment of the laser system, the pixel cells include an electrochromic component with said electrochromic component being a solid layer of electrochromic material sandwiched between two electrode layers. In an alternate embodiment of the invention, the laser system comprises a mask with pixel cells that include a substrate-dispersed liquid crystal material component with a preferred embodiment featuring a plurality of substrate-dispersed liquid crystal material members arranged in series with respect to a path of laser beam travel.
The laser system also preferably features pixel cells that include first, second and third multiple substrate-dispersed liquid crystal members arranged in a stacked, integral relationship and means for generating an electric comprising means for generating an electric field across said second substrate-dispersed member and means for switching between electric field on and electric field off across each of said first and third substrate dispersed layers while said second substrate dispersed member has an electric field thereacross. The laser system also preferably includes pixel state directing means that includes a processor and an interface linking said processor and mask, and said directing means refreshes a pattern in said mask on a refresh cycle of 100 ms or less. The interface device preferably includes means for converting digital information to individual pixel voltage signals.
The present invention also includes a method for ablating a substrate such as the cornea of an eye which includes directing electromagnetic radiation to a mask having a plurality of controllable, electrochromic or a plurality of one layer or more preferably multi-layer substrate-dispersed pixel cells arranged in a predetermined pattern. The method further includes directing transmitted portions of said electromagnetic radiation exiting said mask onto the substrate for ablating the substrate. In a preferred embodiment the method also includes altering a first pattern defined by said pixel cells into a second pattern between pulses of the laser. In addition the method further features the processing of acquired volumetric ablation pattern data to provide pixel cell transmission state control signals to said pixel cells of said mask. The volumetric ablation data can include that of a cornea of an eye whereby the method includes directing laser beam energy through said mask and onto a cornea of an eye for sculpturing the cornea of an eye. The method of the present invention also preferably includes shifting an ablation pattern formed in said mask to conform to an eyetracker monitored shift in position of an eye being ablated.
The present invention also features an electro-optical device, comprising, in series with respect to electromagnetic radiation travel (e.g., visual or ultraviolet light) a first electrode, a first substrate-dispersed liquid crystal member with the first electrode layer deposited thereon (e.g. a pixel array electrode if used in a transmission mask or some other device wherein individually variable cells are desired or a solid sheet if the entire device is to switch from one state to another as in a window), a second electrode layer, a second substrate dispersed liquid crystal member sandwiching the second electrode layer, a third electrode layer, a third substrate dispersed liquid crystal member sandwiching the third electrode layer in conjunction with the second substrate dispersed liquid crystal member, and a fourth electrode deposited on the free side of the third substrate-dispersed liquid crystal member. The electro-optical device further preferably comprises electric field generating means which maintains an electric field across said second substrate-dispersed liquid crystal member and which provides means for switching between on and off electric field states for said first and third substrate-dispersed liquid crystal members. For example, a first voltage source between the second and third electrode layers and a second independent voltage source connected with the first and fourth electrode layers and switchable between voltage on and off states while the first voltage source maintains an electric field across the second substrate-dispersed liquid crystal member This electro-optical device with its presentment of multiple, controlled layers of substrate-dispersed liquid crystal layers with the control preferably being by way of a maintained voltage application to an intermediate layer and a switched voltage application to the layers external to the more intermediate layer also provides an electro-optical device usable in the visible and ultraviolet spectrum for a wide variety of devices such as those presently being used with electrochromic material.
In one embodiment of the invention, the individually adjustable states of transmission are limited to fully transmitting xe2x80x9conxe2x80x9d and fully blocking xe2x80x9coff.xe2x80x9d In another embodiment of the invention, the mask, which is designed for receipt of laser pulses from an excimer laser or the like, further comprises pixel switching timing means for controlling the timing of pixel switching between different on and off states (when desired). In one embodiment, switching takes place in a one-to-one relationship with respect to laser pulses received by the mask. That is, at some time between each pulse, pixel switching activity takes place to alter the pattern presented to the incoming beam of the next pulse.
The mask system of the present invention further includes a pixel switching timing means for timing individual pixel switching between different states and which sets a duty cycle for individual pixels at a duty cycle of from 0% (off for full pulse transmission period) to 100% (on for full transmission period) with at least one or more set pixel duty cycle(s) being at an intermediate value(s) falling between 0 to 100% with respect to the applied or pulse cycle of the main laser beam.
Particularly with electro-optical electrochromic material, it is also possible to change the degree of coloration per pixel by controlling the amount of charge passed through the cell with the degree of color change being fixed upon the switching off of the voltage applied. However, a time based switch over during a particular laser beam pulse cycle with a fixed voltage level can allow for a higher degree of control and is thus more preferable.
The present invention is also directed at a laser system for ophthamological surgery which comprises a laser, and an electro-optical mask having a plurality of individual pixel cells positioned for receiving a laser beam output by the laser. The individual pixel cells of the mask have relatively adjustable transmission states for forming a transmission pattern with respect to the laser beam output by the laser.
The laser system of the present invention further preferably has an expander/collimator assembly that is positioned upstream with respect to the electro-optical mask together with a focusing member positioned downstream from the mask.
The focusing member is designed to focus a latent image pattern formed by the mask onto a projected surface wherein transmitted UV energy of adjacent transmitting pixels is compressed into a minimum overlap relationship (e.g., one involving less than 5% or and more preferably less than 1% overlap) or a minimized spacing relationship (e.g., one involving less that 5% spread apart and more preferably less than 1% spread), or an essentially abutting relationship (of xc2x175% overlap/spacing apart). Preferably the focusing lens is adjustable with respect to the mask and to the focusing plane.
The laser system of the present invention preferably includes directing means for directing pixel transmission state controls to said mask wherein said directing means includes a processor and an interface linking said processor and mask. The processing means preferably further comprises means for processing acquired volumetric ablation volume data and basing pixel control outputs to the mask matrix on the processed acquired volumetric ablation volume data. The laser system also further includes means for acquiring three dimensional volumetric ablation pattern data such as means for receiving corneal ablation data based on topographical and/or aberrometer measurements.
In a preferred embodiment of the invention, the processor farther includes means for segmenting acquired corneal volumetric ablation pattern data into a plurality of matrix segments and means for determining a desired individual pixel transmission status arrangement for respective segments of said acquired volumetric ablation pattern. Preferably all processor functions are handled by a central computer in the laser system of the present invention although sub-processor(s) or sub-processor group(s) are also suited for use in the present invention. The system of the present invention also preferably comprises means for sequentially changing a pixel array pattern based on respective, determined pixel transmission statuses for said segments such as a top to bottom or bottom to top sequence with respect to the ablation segments derived from the acquired volumetric ablation pattern data.
The processor of the laser system is in communication with the mask via an interface device such as a digital interface device for converting digital information to individual pixel voltage signals. The laser system of the present invention preferably also includes means for determining a transmission switching rate for individual pixels of said array based on a duty cycle correlated with a laser pulse period of the laser. For example, individual pixels of the mask are assigned one of two states, either a duty cycle of 0% (no transmission) state during the pulse period state or a 100% (full transmission) state during the pulse period state. In an alternate embodiment, at least some of the individual pixels of the mask are assigned a duty cycle that is intermediate the 0% (no-transmission) state during the pulse period and a 100% (full transmission) state during the pulse period.
A preferred embodiment of the laser system further includes an eyetracker and a processing device which is in communication with both the eyetracker and the mask, and the processing device includes means for implementing a switch or change over in a transmission state of individual pixel shells to shift a pattern defined by pixel cells in said mask form a first pattern position to a second pattern position in correspondence with a shift in location of a projected surface of an eye being monitored by said eyetracker. A similar means can be provided for monitoring and adjusting pixel positions for different types of substrates other than an eye that are subject to movement between laser pulses or refresh states in the mask.
The present invention is also directed at a method for ablating a substrate that comprises directing electromagnetic radiation through an electro-optical mask having a plurality of pixels with individually controllable pixel states, and directing through the electro-optical mask transmitted portions of the electromagnetic radiation onto a substrate such as a corneal surface which receives UV electromagnetic radiation for sculpturing the cornea. The energy is preferably directed through an electro-optical cell that features an electrochromic material to alter the transmission state in a controlled, patterned fashion or through use of a substrate-dispersed liquid crystal material which is preferably a multi-stack of substrate-dispersed layers which block or allow light through depending on the electric field state of the liquid crystal bubbles in each stacked layer.
The method of the present invention further includes altering a first pattern defined by said pixels into a second pattern between pulses of the laser or refreshed states of the mask to alter the ablation pattern on the cornea or exposed substrate. A preferred method of the invention further comprises processing acquired volumetric ablation pattern data to provide pixel transmission state control signals to the individual pixels of the mask. Moreover, the present invention further comprises a method of monitoring any movement of a substrate to be ablated with means for monitoring and, with information obtained from the means for monitoring, shifting the pattern formed in the mask to compensate for a shifting in position of the projected surface prior to the next ablation energy application.